Generally, in the case of providing electrical equipment on a slide body such as a slide seat of a vehicle, used is a power supply device for supplying electric power from a power source such as a battery or the like to the electrical equipment. The power supply device is installed on the vehicle floor. The power supply device is provided with a wire harness used to electrically connect the power source and electrical equipment, and a case for accommodating the wire harness. In this power supply device, the wire harness is accommodated in the case according to the sliding movement of the slide body, or is drawn out from the case (see Japanese Unexamined Patent Application Publication No. 2015-53748).